Implantable acoustic sensor

ABSTRACT

An implantable sound pickup system. The system comprises an intracochlear acoustic sensor implantable in a recipient&#39;s cochlea comprising: an elongate core conductor, and a piezoelectric element disposed on the surface of the core conductor configured to detect pressure waves in the perilymph of the cochlea when the acoustic sensor is at least partially implanted in the cochlea, and to produce electrical signals corresponding to the detected pressure waves.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/986,812, filed Nov. 15, 2004, now U.S. Pat. No.7,580,754, which claims priority from Australian Provisional PatentApplication No. 2003906267, filed Nov. 14, 2003, which are herebyincorporated by reference herein.

BACKGROUND

1. Field of the Invention

The present invention relates generally to acoustic sensors, and moreparticularly, to an implantable acoustic sensor.

2. Related Art

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensorineural. In some cases, a person suffersfrom hearing loss of both types. Conductive hearing loss occurs when thenormal mechanical pathways for sound to reach the cochlea are impeded,for example, by damage to the ossicles. Individuals who suffer fromconductive hearing loss typically have some form of residual hearingbecause the hair cells in the cochlea are undamaged. As a result,individuals suffering from conductive hearing loss typically receive animplantable hearing prosthesis that generates mechanical motion of thecochlea fluid. Some such hearing prostheses, such as acoustic hearingaids, middle ear implants, etc., include one or more componentsimplanted in the recipient, and are referred to herein as implantablehearing prostheses.

In many people who are profoundly deaf, however, the reason for theirdeafness is sensorineural hearing loss. Sensorineural hearing lossoccurs when there is damage to the inner ear, or to the nerve pathwaysfrom the inner ear to the brain. As such, many individuals sufferingfrom sensorineural hearing loss are thus unable to derive suitablebenefit from hearing prostheses that generate mechanical motion of thecochlea fluid. As a result, implantable hearing prostheses that deliverelectrical stimulation to nerve cells of the recipient's auditory systemhave been developed for persons whom do not derive adequate benefit fromconventional hearing aids. Such electrically-stimulating hearingprostheses deliver electrical stimulation to nerve cells of therecipient's auditory system thereby providing the recipient with ahearing percept. Electrically-stimulating hearing prostheses include,for example, auditory brain stimulators and cochlear prostheses(commonly referred to as cochlear prosthetic devices, cochlear implants,cochlear devices, and the like; simply “cochlear implants” herein.)

Oftentimes sensorineural hearing loss is due to the absence ordestruction of the cochlear hair cells which transduce acoustic signalsinto nerve impulses. It is for this purpose that cochlear implants havebeen developed. Cochlear implants provide a recipient with a hearingpercept by delivering electrical stimulation signals directly to theauditory nerve cells, thereby bypassing absent or defective hair cellsthat normally transduce acoustic vibrations into neural activity. Suchdevices generally use an electrode array implanted in the cochlea sothat the electrodes may differentially activate auditory neurons thatnormally encode differential pitches of sound.

Auditory brain stimulators are used to treat a smaller number ofrecipients with bilateral degeneration of the auditory nerve. For suchrecipients, the auditory brain stimulator provides stimulation of thecochlear nucleus in the brainstem.

Totally or fully implantable forms of the above and other implantablehearing prostheses have been developed to treat a recipient'sconductive, sensorineural and/or combination hearing loss. As usedherein, a totally implantable hearing prosthesis refers to animplantable prosthesis that is capable of operating, at least for afinite period of time, without an external device.

SUMMARY

In one aspect of the present invention, an implantable sound pickupsystem is provided. The implantable sound pickup system comprises anintracochlear acoustic sensor implantable in a recipient's cochleacomprising: an elongate core conductor, and a piezoelectric elementdisposed on the surface of the core conductor configured to detectpressure waves in the perilymph of the cochlea when the acoustic sensoris at least partially implanted in the cochlea, and to produceelectrical signals corresponding to the detected pressure waves.

In a still other aspect of the present invention, a cochlear implant isprovided. The cochlear implant comprises: an intracochlear acousticsensor implantable in a recipient's cochlea comprising: an elongate coreconductor, a piezoelectric element disposed on the surface of the coreconductor configured to detect pressure waves in the perilymph of thecochlea when the acoustic sensor is at least partially implanted in thecochlea, and to produce electrical signals corresponding to the detectedpressure waves; and an electrode assembly configured to deliverelectrical stimulation signals, generated based on the electricalsignals produced by the piezoelectric element, to the recipient'scochlea

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described below with referenceto the attached drawings, in which:

FIG. 1 is a perspective view of an exemplary totally implantablecochlear implant, in which embodiments of the present invention may beimplemented;

FIG. 2A is a side view of a totally implantable cochlear implant inaccordance with embodiments of the present invention;

FIG. 2B is a side view of a totally implantable cochlear implant inaccordance with embodiments of the present invention;

FIG. 3 is a side view of a sound pickup system in accordance withembodiments of the present invention, from which sections have beenremoved;

FIG. 4A is a cross-sectional view of the sound pickup system of FIG. 3taken along line 4-4, during a stage of the manufacturing process;

FIG. 4B is a cross-sectional view of the sound pickup system of FIG. 3taken along line 4-4, during a stage of the manufacturing process;

FIG. 4C is a cross-sectional view of the sound pickup system of FIG. 3taken along line 4-4, during a stage of the manufacturing process;

FIG. 4D is a cross-sectional view of the sound pickup system of FIG. 3taken along line 4-4, during a stage of the manufacturing process;

FIG. 4E is a cross-sectional view of the sound pickup system of FIG. 3taken along line 4-4, during a stage of the manufacturing process;

FIG. 5 is a flowchart illustrating the steps performed duringmanufacture of the sound pickup system of FIG. 3;

FIG. 6A is a side view of a sound pickup system in accordance withembodiments of the present invention, from which sections have beenremoved;

FIG. 6B is a side view of a sound pickup system in accordance withembodiments of the present invention, from which sections have beenremoved;

FIG. 6C is a side view of a sound pickup system in accordance withembodiments of the present invention, from which sections have beenremoved;

FIG. 6D is a side view of a sound pickup system in accordance withembodiments of the present invention, from which sections have beenremoved;

FIG. 7 is a functional block diagram of a totally implantable cochlearimplant in accordance with embodiments of the present invention;

FIG. 8 is a schematic diagram of an exemplary charge amplifier inaccordance with embodiments of the present invention; and

FIG. 9 is a schematic diagram illustrating the modeling of apiezoelectric element.

DETAILED DESCRIPTION

Aspects of the present invention are generally directed to animplantable sound pickup system for a hearing prosthesis. Theimplantable sound pickup system includes an intracochlear acousticsensor implantable in a recipient's cochlea, and a cable connecting thesensor to one or more other components of the hearing prosthesis. Theintracochlear acoustic sensor comprises a core conductor, and apiezoelectric element disposed on the surface of the core conductor. Thepiezoelectric element is configured to detect pressure waves in thecochlea fluid when the core conductor is at least partially implanted inthe cochlea, and to produce electrical signals corresponding to thedetected pressure waves.

In certain embodiments, the sound pickup system is a component of atotally or fully implantable cochlear prosthesis (commonly referred toas a cochlear prosthetic device, cochlear implant, cochlear device, andthe like; simply “cochlear implants” herein). As noted, theintracochlear acoustic sensor detects an acoustic sound signal throughmovement of the cochlea fluid, and generates corresponding electricalsignals. The cochlear implant further comprises an electrode assemblythat delivers to the recipient's cochlea electrical stimulation signalsgenerated based on the acoustic signals detected by the sensor.

Embodiments of the present invention will be primarily described withreference to the use of the sound pickup system in a cochlear implant.It would be appreciated that the sound pickup system may also beimplemented any partially or fully implantable hearing prosthesis nowknown or later developed, including, but not limited to, acoustichearing aids, auditory brain stimulators, middle ear mechanicalstimulators, hybrid electro-acoustic prosthesis or other prosthesis thatelectrically, acoustically and/or mechanically stimulate components ofthe recipient's outer, middle or inner ear.

FIG. 1 is perspective view of a totally implantable cochlear implant,referred to as cochlear implant 100, implanted in a recipient. Therecipient has an outer ear 101, a middle ear 105 and an inner ear 107.Components of outer ear 101, middle ear 105 and inner ear 107 aredescribed below, followed by a description of cochlear implant 100.

In a fully functional ear, outer ear 101 comprises an auricle 110 and anear canal 102. An acoustic pressure or sound wave 103 is collected byauricle 110 and channeled into and through ear canal 102. Disposedacross the distal end of ear cannel 102 is a tympanic membrane 104 whichvibrates in response to sound wave 103. This vibration is coupled tooval window or fenestra ovalis 112 through three bones of middle ear105, collectively referred to as the ossicles 106 and comprising themalleus 108, the incus 109 and the stapes 111. Bones 108, 109 and 111 ofmiddle ear 105 serve to filter and amplify sound wave 103, causing ovalwindow 112 to articulate, or vibrate in response to vibration oftympanic membrane 104. This vibration sets up waves of fluid motion ofthe perilymph within cochlea 140. Such fluid motion, in turn, activatestiny hair cells (not shown) inside of cochlea 140. Activation of thehair cells causes appropriate nerve impulses to be generated andtransferred through the spiral ganglion cells (not shown) and auditorynerve 114 to the brain (also not shown) where they are perceived assound.

As shown, cochlear implant 100 comprises one or more components whichare temporarily or permanently implanted in the recipient. Cochlearimplant 100 is shown in FIG. 1 with an external device 142 which isconfigured to provide power to the cochlear implant.

In the illustrative arrangement of FIG. 1, external device 142 comprisesa power source (not shown) disposed in a Behind-The-Ear (BTE) unit 126.External device 142 also includes components of a transcutaneous energytransfer link, collectively referred to as an external energy transferassembly. The transcutaneous energy transfer link is used to transferpower and/or data to cochlear implant 100. As would be appreciated,various types of energy transfer, such as infrared (IR),electromagnetic, capacitive and inductive transfer, may be used totransfer the power and/or data from external device 142 to cochlearimplant 100. In the illustrative embodiments of FIG. 1, the externalenergy transfer assembly comprises an external coil 130 that forms partof an inductive radio frequency (RF) communication link. External coil130 is a wire antenna coil comprised of multiple turns of electricallyinsulated single-strand or multi-strand platinum or gold wire. Externaldevice 142 also includes a magnet (not shown) positioned within theturns of wire of external coil 130. It should be appreciated that theexternal device shown in FIG. 1 is merely illustrative, and otherexternal devices may be used with embodiments of the present invention.

Cochlear implant 100 comprises an internal energy transfer assembly 132which may be positioned in a recess of the temporal bone adjacentauricle 110 of the recipient. Internal energy transfer assembly 132 is acomponent of the transcutaneous energy transfer link and receives powerand/or data from external device 142. In the illustrative embodiment,the energy transfer link comprises an inductive RF link, and internalenergy transfer assembly 132 comprises a primary internal coil 136.Internal coil 136 is typically a wire antenna coil comprised of multipleturns of electrically insulated single-strand or multi-strand platinumor gold wire.

Cochlear implant 100 comprises a main implant module 120. In embodimentsof the present invention, internal energy transfer assembly 132 andimplant module 120 are hermetically sealed within a biocompatiblehousing.

Cochlear implant 100 further comprises an intracochlear acoustic sensor150 connected to implant module 120 via a cable 152. As shown, cable 152has a proximal end connected to implant module 120, and a distal endconnector to intracochlear acoustic sensor 150 positioned in cochlea140. Cable 152 extends from implant module 120 to intracochlear acousticsensor 150 through mastoid bone 119. As described below, cable 152 andintracochlear acoustic sensor 150 are collectively referred to as asound pickup system.

In the embodiments of FIG. 1, intracochlear acoustic sensor 150 isdisposed in basal region 116 of cochlea 140. An electrode assembly 118extends from the distal end of intracochlear acoustic sensor 150 towardsthe apical end of cochlea 140, referred to as cochlea apex 134.Electrode assembly 118 comprises a longitudinally aligned and distallyextending array 146 of electrodes 148, sometimes referred to aselectrode array 146 herein, disposed along a length thereof. Althoughelectrode array 146 may be disposed on electrode assembly 118, in mostpractical applications, electrode array 146 is integrated into electrodeassembly 118. As such, electrode array 146 is referred to herein asbeing disposed in electrode assembly 118.

In the embodiments of FIG. 1, electrode assembly 118 and the soundpickup system are integrated with one another and form a singleimplantable component. As described in greater detail below, inalternative embodiments of the present invention the sound pickup systemand electrode assembly 118 comprise physically separate and independentcomponents.

Intracochlear acoustic sensor 150 and electrode assembly 118 may beinserted into cochlea 140 via a cochleostomy 122. In othercircumstances, a cochleostomy may be formed through round window 121,oval window 112, the promontory 123, etc.

As described in detail below, intracochlear acoustic sensor 150 isconfigured to receive sounds by detecting pressure waves in therecipient's inner ear fluid, such as the perilymph. More specifically,an acoustic pressure or sound wave 103 is collected by auricle 110 andchanneled through ear canal 102, resulting in the vibration of tympanicmembrane 104. The vibration of tympanic membrane 104 is coupled to ovalwindow 112 through bones 108, 109 and 111 of middle ear 105, causingoval window 112 to vibrate. This vibration sets up waves of fluid motionof the perilymph, referred to herein as pressure waves, within cochlea140 that are detected by intracochlear acoustic sensor 150. As describedbelow, intracochlear acoustic sensor 150 produces electrical signalscorresponding to the detected pressure waves, and relays the electricalsignals to implant module 120 via cable 152. In certain embodiments, theelectrical signals provided to implant module 120 are current signalsthat are converted to voltage signals by a charge amplifier (not shown).These voltage signals are provided to a processing module (also notshown) in implant module 120 that generates data signals correspondingto the received sound. The data signals are provided to a stimulatorunit (also not shown) which generates electrical stimulation signalsbased on the data signals. The electrical stimulation signals aredelivered to the recipient via electrode assembly 118, thereby evokingperception of the received sound signals by the recipient.

As noted, cochlear implant 100 comprises a totally implantableprosthesis that is capable of operating, at least for a period of time,without the need for external device 142. Therefore, cochlear implant100 further comprises a rechargeable power source (not shown) thatstores power received from external device 142. The power source maycomprise, for example, a rechargeable battery. During operation ofcochlear implant 100, the power stored by the power source isdistributed to the various other implanted components as needed. Thepower source may be located in implant module 120, or disposed in aseparate implanted location.

FIGS. 2A and 2B are side views of embodiments of cochlear implant 100 ofFIG. 1, referred to as cochlear implants 200A and 200B, respectively.Cochlear implants 200A and 200B each comprise an implant module 220 thatis substantially similar to implant module 120 described above withreference to FIG. 1. Specifically, implant modules 220 comprise variouselectronic components (i.e. processing module, stimulator unit, etc.)hermetically sealed in a housing 222 with components of an internalenergy transfer assembly 132 (FIG. 1). For ease of illustration, onlyreceiver coil 240 of internal energy transfer assembly 132 is shown inFIGS. 2A and 2B.

Cochlear implant 200A of FIG. 2A has an elongate electrode assembly 228extending from implant module 220. Similar to electrode assembly 118 ofFIG. 1, electrode assembly 228 comprises a longitudinally aligned anddistally extending array of electrodes. Electrode assembly 228 has aproximal end connected to implant module 220, and a distal endconfigured to be implanted in a recipient's cochlea. In some embodimentselectrode assembly 228 may be implanted at least in a recipient's basalregion, and sometimes further. For example, electrode assembly 228 mayextend towards the apical end of the recipient's cochlea. In certaincircumstances, electrode assembly 228 may be inserted into the cochleavia a cochleostomy formed through the round window, oval window, thepromontory 123, etc. It would be appreciated that electrode assembly 228is inserted into the cochlea so as have minimal impact on the flow ofthe cochlea fluid. That is, the electrode assembly 228 is implanted soas not to disturb, or to have minimal effect on, cochlea hydrodynamics.

Cochlear implant 200A further includes a sound pickup system 280comprising an intracochlear acoustic sensor 250 for detecting sound, anda cable 252 connecting the sensor to implant module 220. As explainedabove, an acoustic pressure or sound wave is collected by therecipient's auricle and channeled through the ear canal, causingvibration of the tympanic membrane. This vibration is transferred fromthe tympanic membrane to the recipient's oval window through the bonesof the middle ear, causing the oval window to vibrate. The vibration ofthe oval window sets up pressures waves within the cochlea perilymphthat are detected by intracochlear acoustic sensor 250. As described ingreater detail below, intracochlear acoustic sensor 250 produceselectrical signals corresponding to the detected pressure waves. Theseelectrical signals are relayed to implant module 120 via cable 252.Similar to electrode assembly 228, intracochlear acoustic sensor 250 isimplanted so as not to disturb, or to have minimal effect on, cochleahydrodynamics.

In the embodiments of FIG. 2A, electrode assembly 228 and intracochlearsensor 250 are physically separate components that may be independentlyimplanted in a recipient's cochlea. FIG. 2B illustrates embodiments inwhich a sound pickup system 290 and an electrode assembly 218 comprise aunitary, integrated component. More specifically, in the embodiments ofFIG. 2B intracochlear acoustic sensor 260 is configured to be implantedin the basal region of a recipient's cochlea, and electrode assembly 218extends from the distal end of the sensor. In such embodiments, theelectrical connections between the electrodes (not shown) of electrodeassembly 218 and implant module 220 may extend through or aroundintracochlear acoustic sensor 260 through cable 262. Because soundpickup system 290 and electrode assembly 218 comprise an integratedcomponent, only one cochlea insertion procedure is required duringsurgery. Similar to the embodiments of FIG. 2A, sound pickup system 290and electrode assembly 218 are inserted into the cochlea so as not todisturb, or to have minimal effect on, cochlea hydrodynamics.

As described above, intracochlear acoustic sensor 260 senses sound bydetecting pressures waves within the cochlea perilymph. Intracochlearacoustic sensor 260 produces electrical signals corresponding to thedetected pressure waves, and relays the electrical signals to implantmodule 220 via cable 262.

The embodiments of FIG. 2B further illustrate the use of a sealingmember 254 disposed about cable 262. Sealing member 262 is configured tobe positioned outside the cochlea and is operatively in contact with theexternal wall of the cochlea to seal perilymph inside the cochlea. Incertain embodiments, sealing member 254 is made from a biocompatiblematerial such as titanium. It would be appreciated that electrodeassembly 218 and intracochlear acoustic sensor 260 may, in certaincircumstances, be implanted in a recipient so as to seal the cochleawithout the need for sealing member 254. It would also be appreciatedthat similar sealing members may used in the embodiments of FIG. 2A toseal the openings in the cochlea through which cable 252 and electrodeassembly 228 extend.

FIG. 3 is a side view of one embodiment of a sound pickup system 380A inaccordance with aspects of the present invention. As described below,sections of sound pickup system 380A are removed to illustrate allelements of the system.

In the illustrative embodiments of FIG. 3, sound pickup system 380Acomprises an intracochlear acoustic sensor 350A, and a cable 352A formedinto a integrated component. Sound pickup system 380A includes anelongate core conductor 360A extends through both of sensor 350A andcable 352A. Core conductor 360A comprises an elongate metallic element,such as, for example, platinum, titanium, or other type of conductivewire. Disposed on the surface of core conductor 360A is a piezo-polymerlayer 362. Piezo-polymer layer 362 is formed from a material that, whenpolarized, displays the piezoelectric effect. That is, the polarizedregion of piezo-polymer layer 362 produces an electrical signal upon theimposition of a mechanical stress or strain to the layer. As describedbelow, pressure waves within a recipient's cochlea cause a mechanicalstress on piezo-polymer layer 362. The mechanical stress causes thepolarized region of piezo-polymer layer 362 to generate electricalsignal corresponding to the detected pressure waves.

As used herein, piezoelectric materials usable in embodiments of thepresent invention include piezo-polymers, piezoceramics and any othersuitable material that may be polarized to exhibit the piezoelectriceffect. For example, in certain embodiments of the present inventionpiezoelectric element 362 comprises a piezo-polymer layer 362 such aspolyvinylidene fluoride (PVDF) or a PVDF copolymer such as P(VDF-TrFE).

As shown, in the embodiments of FIG. 3 piezo-polymer layer 362 is aunitary layer disposed circumferentially about the length of coreconductor 360A. In alternative embodiments piezo-polymer layer 362comprises a piezoelectric tape spirally wrapped around core conductor360A.

Also as shown in FIG. 3, a surface electrode 364 is disposed onpiezo-polymer layer 362. Surface electrode 364 is a thin metallicelement that functions as a ground electrode and as an electromagneticinterference (EMI) shield. Surface electrode 364 may be a thin filmlayer formed from any suitable biocompatible conductive material suchas, for example, titanium, platinum, gold, or other material. A thinexternal passivation layer 366 is disposed on the outer surface ofsurface electrode 364 to electrically isolate surface electrode 364 fromthe surrounding cochlea fluid. External layer 366 may be formed from anysuitable biocompatible insulative material such as parylene or siliconrubber.

In embodiments of FIG. 3A, piezo-polymer layer 362, surface electrode364 and external layer 366 each circumferentially surround coreconductor 360A, or the previously applied layer, and substantiallyextend the length of core conductor 360A. As shown in FIGS. 4A-4E, aproximal end of core conductor 360A remains exposed to permit soundpickup system 380A to be connected to an additional component, such asan implant module.

As noted above, a selected section of piezo-polymer layer 362 ispolarized. In the embodiments of FIG. 3A, the distal region ofpiezo-polymer layer 362 is polarized, and is referred to as polarizedregion 370. The remainder of piezo-polymer layer 362 remains unpolarizedand is referred to as unpolarized region 372. When implanted in arecipient's cochlea, polarized region 370 detects pressure waves in thecochlea fluid, and generates electrical signals representative of thepressure waves. These electrical signals are relayed through coreconductor 360A to the implant module. The section of sound pickup system380A containing polarized region 370 is referred to herein asintracochlear acoustic sensor 350A, while the remainder of sound pickupsystem 380A is referred to as cable 352A.

As noted, the electrical signals generated by polarized region 370 ofpiezo-polymer layer 362 are relayed to implant module via core conductor360A. In certain embodiments, the relayed electrical signals are currentsignals that are converted to voltage signals by a charge amplifier (notshown) in the implant module. An exemplary charge amplifier is describedbelow with reference to FIG. 8.

In specific embodiments of the present invention, only intracochlearacoustic sensor 350A is implanted in the recipient's cochlea. Inalternative embodiments, a portion of cable 352A is also implanted inthe cochlea. In further embodiments, only a portion of intracochlearacoustic sensor 350A is implanted in the cochlea.

As would be appreciated, intracochlear acoustic sensor 350A is implantedthrough a natural or artificial opening in the recipient's cochlea.Intracochlear acoustic sensor 350A is also implanted so as to haveminimal impact on the cochlear fluid dynamics. In certain embodiments,the natural or artificial opening through which sensor 350A is insertedshould be sealed so as to reduce the impact on the fluid flow.Therefore, as noted above with reference to FIGS. 2A and 2B, in certainembodiments intracochlear sensor 350A and/or cable 352A may beconfigured to seal the opening through which sensor 350A is inserted. Inalternative embodiments, a sealing member may be positioned on thesurface of intracochlear sensor 350A or on the surface of cable 352A toseal the opening.

FIGS. 4A-4E are cross-sectionals views of sound pickup system 380A ofFIG. 3 during various stages of the manufacturing process. The views ofFIGS. 4A-4E are taken along cross-sectional line 4-4 of FIG. 3.Similarly, FIG. 5 is a flowchart illustrating a manufacturing process500 used to form sound pickup system 380A. For ease of illustration,manufacturing process 500 of FIG. 5 will be described with reference toFIGS. 4A-4E.

In embodiments of the present invention, a core conductor 360A is firstprovided. FIG. 4A is a cross-sectional view of an exemplary coreconductor 360 formed from a platinum wire. In specific embodiments ofthe present invention, the platinum core conductor 360A has a circularcross-section. It would be appreciated that a core conductor havingother cross-sectional shapes and different dimensions may also be used.

At block 502, the surface of a portion of core conductor 360A is coatedwith piezo-polymer layer 362. As shown in FIG. 4B, piezo-polymer layer362 circumferentially extends around the surface of core conductor 360A.Also as shown in FIG. 4B, piezo-polymer layer 362 is disposed on coreconductor 360A such that distal end 430 is fully coated, but thatproximal end 432 remains uncoated.

At block 504, a region of piezo-polymer layer is polarized using, forexample, corona or plasma polarization methods. In the specificembodiments of FIG. 4C, the distal region of the piezo-polymer layer 362is polarized to form polarized region 370. The remainder ofpiezo-polymer layer 362 remains unpolarized and is referred to asunpolarized region 372. For ease of illustration polarized region 370and unpolarized region 372 are not differentiated in FIGS. 4D and 4E.

At block 506, the surface of piezo-polymer layer 362 is coated with anelectrode layer, referred to as surface electrode 364. As shown in FIG.4D, surface electrode 364 extends circumferentially about piezo-polymerlayer 362, and covers the distal end thereof. However, as noted abovethe proximal end 432 of core conductor 360A remains exposed. In thespecific embodiments illustrated in FIG. 4D, surface electrode 364comprises a metallic thin film layer made from gold, platinum or othermaterial. Surface electrode 364 is sputtered onto the surface of thepiezo-polymer layer 362. It would be appreciated that this step can beperformed prior to, or after, connection of core conductor 360A to animplant module.

At block 508, the surface of surface electrode 364 is coated with anexternal passivation layer 366. As shown in FIG. 4E, external layer 366extends circumferentially about surface electrode 364, and covers thedistal end thereof. However, as noted above the proximal end 432 of coreconductor 360A remains exposed. In the embodiments of FIG. 4E, externallayer 366 comprises a thin layer of parylene that substantially freefrom holes, and which conforms to the outer surface of surface electrode364.

It would be appreciated that the embodiments of FIGS. 4A-4E are merelyillustrative and are not shown to scale. It would also be appreciatedthat the thickness of the various layers of FIGS. 4A-4E, or the relativethickness of layers to one another is not indicative of the thicknessutilized in embodiments of the present invention

FIG. 6A is a partial cross-sectional view of one embodiment of a soundpickup system 380B in accordance with aspects of the present invention.As shown, sound pickup system 380B comprises an intracochlear acousticsensor 350B, and a cable 352B. An elongate core conductor 360B that issubstantially the same as core conductor 360A of FIG. 3 extens throughacoustic sensor 350B. However, unlike core conductor 360A of FIG. 3,core conductor 360B does not extend through cable 352B.

In the embodiments of FIG. 6A, core conductor 360B is coated with apiezo-polymer layer 362. Although FIG. 6A illustrates the use ofpiezo-polymer 362, it would be appreciated that other piezoelectricelements may also be used in alternative embodiments. Intracochlearacoustic sensor 350B also comprises a surface electrode 364 disposed onthe surface of piezo-polymer layer 362, and a thin external passivationlayer 366 disposed on the surface of surface electrode 364. Surfaceelectrode 364 and external layer 366 are again implemented as describedabove with reference to FIG. 3.

As shown in FIG. 6A, piezo-polymer layer 362, surface electrode 364 andexternal layer 366 each circumferentially surround core conductor 360B,or the previously applied layer, and extend at least the length of coreconductor 360B. However, as noted above, core conductor 360B does notextend through cable 352B. Rather, a wire 682 is connected to theproximal end of core conductor 360B. Wire 682 is embedded in a flexiblecoating 668 such as a flexible silicone rubber. Flexible coating 668extends from the proximal end of piezo-polymer layer 362 to adjacent theproximal end of wire 682. The proximal end of wire 682 remains exposedfor electrical connection with an implant module.

In the embodiments of FIG. 6A, flexible coating 668 is disposed aboutwire 682 so that the outer dimensions of flexible coating 668 aresubstantially the same as the outer dimensions of piezo-polymer layer362, and surface electrode 364 is disposed on the outer surface thereof.Similarly, external layer 366 is disposed on the outer surface ofsurface electrode 364.

As shown in FIG. 6A, all of piezo-polymer layer 362 is polarized so asto generate electrical signals representative of detected pressurewaves. These electrical signals are relayed through core conductor 360Bto wire 682 where they are provided to the implant module. The sectionof sound pickup system 380B containing polarized piezo-polymer layer 362is referred to herein as intracochlear acoustic sensor 350B, while theremainder of sound pickup system 380B is referred to as cable 352B.

As noted above, cable 352B comprises wire 682 embedded in flexiblecoating 668. As shown, a section of wire 682 is formed into a helicalshape and comprises a plurality of coils 674. Coils 674 provide strainrelief to sound pickup system 380B. Specifically, coils 674 are embeddedin flexible coating 668 to provide elongation of wire 682 if cable 352Bis bent or otherwise subjected to external forces. This strain reliefreduces the risk of the breakage of the electrical connection between animplant module and intracochlear sensor 350B in response to suchflexing/bending of cable 352B.

As noted, the electrical signals generated by polarized piezo-polymerlayer 362 are relayed to implant module via core conductor 360B and wire682. In certain embodiments, the relayed electrical signals are currentsignals that are converted to voltage signals by a charge amplifier (notshown) in the implant module. An exemplary charge amplifier is describedbelow with reference to FIG. 8.

In specific embodiments of the present invention, only intracochlearacoustic sensor 350B is implanted in the recipient's cochlea. Inalternative embodiments, a portion of cable 352B is also implanted inthe cochlea. In still other embodiments, only a portion of acousticsensor 350B is implanted in the cochlea.

As would be appreciated, intracochlear acoustic sensor 350B is implantedthrough a natural or artificial opening in the recipient's cochlea.Intracochlear acoustic sensor 350B is also implanted so as to haveminimal impact on the cochlear fluid dynamics. In certain embodiments,the natural or artificial opening through which sensor 350B is insertedshould be sealed so as to reduce the impact on the fluid flow.Therefore, as noted above with reference to FIGS. 2A and 2B, in certainembodiments intracochlear sensor 350B and/or cable 352B may beconfigured to seal the opening through which sensor 350B is inserted. Inalternative embodiments, a sealing member may be positioned on thesurface of intracochlear sensor 350B or on the surface of cable 352B toseal the opening.

FIG. 6B is a partial cross-sectional view of another embodiment of asound pickup system 380C in accordance with aspects of the presentinvention. As shown, sound pickup system 380C comprises intracochlearacoustic sensor 350C, and cable 352C. Sound pickup system 380C furthercomprises an elongate core conductor 360C that extends through bothsensor 350C and cable 352C. In the embodiments of FIG. 6B, coreconductor 360C comprises a bundle of, for example, a platinum, titanium,gold or other type of conductive wires 690. Wires 690 may each comprisesingle or multi-strand wires.

Similar to the embodiments of FIG. 3, core conductor 360C is coated witha piezo-polymer layer 362. Sound pickup system 380C also comprises asurface electrode 364 disposed on the surface of piezo-polymer layer362, and a thin external passivation layer 366 disposed on the outersurface of surface electrode 364. Surface electrode 364 and externallayer 366 are again implemented as described above with reference toFIG. 3.

As shown in FIG. 6A, piezo-polymer layer 362, surface electrode 364 andexternal layer 366 each circumferentially surround core conductor 360B,or the previously applied layer, and extend the length of core conductor360C. Similar to the embodiments described above with reference to FIGS.4A-4E, a proximal end of core conductor 360C remains exposed to permitsound pickup system 380C to be connected to an additional component,such as an implant module.

As described above, a selected section of piezo-polymer layer 362 ispolarized. In the embodiments of FIG. 3A, the distal region ofpiezo-polymer layer 362 is polarized and is referred to as polarizedregion 370. The remainder of piezo-polymer layer 362 remains unpolarizedand is referred to as unpolarized region 372. When implanted in arecipient's cochlea, polarized region 370 detects pressure waves in thecochlea fluid, and generates electrical signals representative of thepressure waves. These electrical signals are relayed through coreconductor 360C to the implant module. The section of sound pickup system380C containing polarized region 370 is referred to herein asintracochlear acoustic sensor 350C, while the remainder of sound pickupsystem 380C is referred to as cable 352C.

As noted, the electrical signals generated by polarized region 370 ofpiezo-polymer layer 362 are relayed to implant module via core conductor360C. In certain embodiments, the relayed electrical signals are currentsignals that are converted to voltage signals by a charge amplifier (notshown) in the implant module. An exemplary charge amplifier is describedbelow with reference to FIG. 8.

As would be appreciated, intracochlear acoustic sensor 350C is implantedthrough a natural or artificial opening in the recipient's cochlea.Intracochlear acoustic sensor 350C is also implanted so as to haveminimal impact on the cochlear fluid dynamics. In certain embodiments,the natural or artificial opening through which sensor 350C is insertedshould be sealed so as to reduce the impact on the fluid flow.Therefore, as noted above with reference to FIGS. 2A and 2B, in certainembodiments intracochlear sensor 350C and/or cable 352C may beconfigured to seal the opening through which sensor 350C is inserted. Inalternative embodiments, a sealing member may be positioned on thesurface of intracochlear sensor 350C or on the surface of cable 352C toseal the opening.

FIG. 6C is a partial cross-sectional view of a still other embodiment ofa sound pickup system 380D in accordance with aspects of the presentinvention. As shown, sound pickup system 380D comprises intracochlearacoustic sensor 350D, and cable 352D. Sound pickup system 380D includesan elongate core conductor 360D that extends the through sensor 350D andcable 352D. In the embodiments of FIG. 6C, core conductor 360D comprisesa non-conductive core 678 having a thin metallic film 676 disposed onthe surface thereof. Metallic film 676 is sometimes referred to hereinas inner signal electrode 676. Non-conductive core 678 may comprise aflexible polymer material, while inner signal electrode 676 comprises alayer of, for example, platinum, titanium, gold or other conductivematerial.

Similar to the embodiments described above, core conductor 360D iscoated with a piezo-polymer layer 362. Sound pickup system 380D alsocomprises a surface electrode 364 disposed on the surface ofpiezo-polymer layer 362, and a thin external passivation layer 366disposed on the outer surface of surface electrode 364. Surfaceelectrode 364 and external layer 366 are again implemented as describedabove with reference to FIG. 3.

As shown in FIG. 6A, piezo-polymer layer 362, surface electrode 364 andexternal layer 366 each circumferentially surround core conductor 360B,or the previously applied layer, and extend the length of core conductor360D. Similar to the embodiments described above with reference to FIGS.4A-4E, a proximal end of core conductor 360D remains exposed to permitsound pickup system 380D to be connected to an additional component,such as an implant module.

As described above, a selected section of piezo-polymer layer 362 ispolarized. In the embodiments of FIG. 3A, the distal region ofpiezo-polymer layer 362 is polarized and is referred to as polarizedregion 370. The remainder of piezo-polymer layer 362 remains unpolarizedand is referred to as unpolarized region 372. When implanted in arecipient's cochlea, polarized region 370 detects pressure waves in thecochlea fluid, and generates electrical signals representative of thepressure waves. These electrical signals are relayed through coreconductor 360D to the implant module. The section of sound pickup system380D containing polarized region 370 is referred to herein asintracochlear acoustic sensor 350D, while the remainder of sound pickupsystem 380D is referred to as cable 352D.

The electrical signals generated by polarized region 370 ofpiezo-polymer layer 362 are relayed to implant module via inner signalelectrode 676 of core conductor 360D. In certain embodiments, therelayed electrical signals are current signals that are converted tovoltage signals by a charge amplifier (not shown) in the implant module.An exemplary charge amplifier is described below with reference to FIG.8.

As would be appreciated, intracochlear acoustic sensor 350D is implantedthrough a natural or artificial opening in the recipient's cochlea.Intracochlear acoustic sensor 350D is also implanted so as to haveminimal impact on the cochlear fluid dynamics. In certain embodiments,the natural or artificial opening through which sensor 350D is insertedshould be sealed so as to reduce the impact on the fluid flow.Therefore, as noted above with reference to FIGS. 2A and 2B, in certainembodiments intracochlear sensor 350D and/or cable 352D may beconfigured to seal the opening through which sensor 350D is inserted. Inalternative embodiments, a sealing member may be positioned on thesurface of intracochlear sensor 350D or on the surface of cable 352D toseal the opening.

FIG. 6D is a partial cross-sectional view of one embodiment of a soundpickup system 380E in accordance with aspects of the present invention.As shown, sound pickup system 380E comprises intracochlear acousticsensor 350E and cable 352E. Sound pickup system 380E also includes anelongate core conductor 360E. Core conductor 360E comprises an elongateporous core 680 formed from, for example, polyurethane. Disposed on thesurface of porous core 680 is a thin metallic film 676. Metallic film676 is sometimes referred to herein as inner signal electrode 676 andcomprises a layer of, for example, platinum, titanium, gold or otherconductive material.

Similar to the embodiments of FIG. 3, core conductor 360E is coated witha thin film piezo-polymer layer 362. Sound pickup system 380E alsocomprises a surface electrode 364 disposed on the surface ofpiezo-polymer layer 362, and a thin external passivation layer 366disposed on the outer surface of surface electrode 364. Surfaceelectrode 364 and external layer 366 are again implemented as describedabove with reference to FIG. 3.

As shown in FIG. 6D, piezo-polymer layer 362, surface electrode 364 andexternal layer 366 each circumferentially surround core conductor 360E,or the previously applied layer, and extend at least the length of coreconductor 360E. In contrast to the embodiments described above, coreconductor 360E does not extend through cable 352E. Rather, a wire 682 isconnected to the proximal end of core conductor 360E. Wire 682 isembedded in a flexible coating 668 such as a flexible silicone rubber.Flexible coating 668 extends from the proximal end of piezo-polymerlayer 362 to adjacent the proximal end of wire 682. The proximal end ofwire 682 remains exposed for electrical connection with an implantmodule.

In the embodiments of FIG. 6D, flexible coating 668 is disposed aboutwire 682 so that the outer dimensions of flexible coating 668 aresubstantially the same as the outer dimensions of piezo-polymer layer362, and surface electrode 364 is disposed on the outer surface thereof.Similarly, external layer 366 is disposed on the outer surface ofsurface electrode 364.

As shown in FIG. 6D, all or substantially all of piezo-polymer layer 362is polarized so as to generate electrical signals representative ofdetected pressure waves. These electrical signals are relayed throughcore conductor 360E to wire 682 where they are provided to the implantmodule. The section of sound pickup system 380E containing polarizedpiezo-polymer layer 362 is referred to herein as intracochlear acousticsensor 350E, while the remainder of sound pickup system 380E is referredto as cable 352E.

As noted above, cable 352E comprises wire 682 embedded in flexiblecoating 668. As shown, a section of wire 682 is formed into a helicalshape and comprises a plurality of coils 674. Coils 674 provide strainrelief to sound pickup system 380E. Specifically, coils 674 are embeddedin flexible coating 668 to provide elongation of wire 682 if cable 352Eis bent or otherwise subjected to external forces. This strain reliefreduces the risk of the breakage of the electrical connection between animplant module and intracochlear sensor 350E in response to suchflexing/bending of cable 352E.

As noted, the electrical signals generated by polarized piezo-polymerlayer 362 are relayed to implant module via core conductor 360E and wire682. In certain embodiments, the relayed electrical signals are currentsignals that are converted to voltage signals by a charge amplifier (notshown) in the implant module. An exemplary charge amplifier is describedbelow with reference to FIG. 8.

In specific embodiments of the present invention, only intracochlearacoustic sensor 350E is implanted in the recipient's cochlea. Inalternative embodiments, a portion of cable 352E is also implanted inthe cochlea.

As would be appreciated, intracochlear acoustic sensor 350E is implantedthrough a natural or artificial opening in the recipient's cochlea.Intracochlear acoustic sensor 350E is also implanted so as to haveminimal impact on the cochlear fluid dynamics. In certain embodiments,the natural or artificial opening through which sensor 350E is insertedshould be sealed so as to reduce the impact on the fluid flow.Therefore, as noted above with reference to FIGS. 2A and 2B, in certainembodiments intracochlear sensor 350E and/or cable 352E may beconfigured to seal the opening through which sensor 350E is inserted. Inalternative embodiments, a sealing member may be positioned on thesurface of intracochlear sensor 350E or on the surface of cable 352E toseal the opening.

In the embodiments of FIG. 6D, the generally cylindrical structure ofintracochlear sensor 350E has a slight curvature through its length sothat the diameter at the mid-section 631 is smaller than that of theends 632, 634. That is, intracochlear acoustic sensor 350E has ahourglass shape. In alternative embodiments, the intracochlear sensor350E has a slight curvature through its length so that the diameter atthe mid-section 631 is larger than that of the ends 632, 634.

FIG. 7 is a functional block diagram of one embodiment of cochlearimplant 100, referred to herein as cochlear implant 700. In theembodiments of FIG. 7, cochlear implant 700 is totally implantable; thatis, all components of cochlear implant 700 are configured to beimplanted under the skin/tissue of a recipient. Because all componentsof cochlear implant 700 are implantable, cochlear implant 700 operates,for at least a period of time, without the need of an external device.

As shown, cochlear implant 700 comprises a main implantable component,referred to as implant module 720. Implant module 720 includes areceiver unit 704, a processing module 706, a stimulator unit 708 and acharge amplifier 710. The embodiments of FIG. 7 are illustrative, and itwould be appreciated that implant module may comprise one or moreadditional components. For example, it would be appreciated that implantmodule 720 may comprise an internal power source, such as a rechargeablebattery, to provide power to the other components of cochlear implant700.

As shown in FIG. 7, receiver unit 704 comprises an internal energytransfer assembly that receives power and/or data from an externaldevice. In certain embodiments, receiver unit 704 may further be atransceiver unit that is configured to transmit data to an externaldevice as well receive power and/or data from an external device.

As shown, cochlear implant 700 further comprises a sound pickup system780 electrically connected to charge amplifier 710 in implant module720. As described elsewhere herein, sound pickup system 780 comprises anintracochlear acoustic sensor 750, and a cable 752. As described indetail above, intracochlear acoustic sensor 750 is configured to sense asound by detecting pressure waves with the recipient's cochlea fluid.Specifically, intracochlear acoustic sensor 750 converts detectedpressure waves into an electrical signal that is related to chargeamplifier 710 via cable 752. In the embodiments of FIG. 7, the proximalend of cable 752 is connected to charge amplifier via a feed through(not shown) extending through the exterior wall of implant module 720.

As explained below, charge amplifier 710 is configured to convert theelectrical charge transferred along cable 752 from sensor 750 into anoutput voltage 730. This output voltage is provided to processing module706. Using voltage output 730, processing module implements one or morespeech processing and/or coding strategies to generate processed datasignals 732 that are provided to a stimulator unit 708. Based on datasignals 732, stimulator unit 708 generates electrical stimulationsignals 734 for delivery to the cochlea of the recipient via electrodes(not shown) of electrode assembly 728. In the illustrative embodiment ofFIG. 7, electrode assembly 728 is physically separate from sound pickupsystem 780. As described above, in an alternative embodiment electrodeassembly 728 and sound pickup system 780 may be integrated into a singlecomponent.

FIG. 8 is a schematic diagram of one embodiment of charge amplifier 710illustrated above in FIG. 7. As noted, charge amplifier 710 may bepositioned within implant module 710 and is connected to intracochlearacoustic sensor 750 via a feed through and cable 752. More specifically,the electrical charge generated by the piezoelectric element ofintracochlear acoustic sensor 750 is relayed through cable 752 to chargeamplifier 710. Charge amplifier 710 converts this related electricalcharge into a voltage output. In embodiments of the present invention,the voltage output by charge amplifier 710 is dependent only on itsfeedback capacitance and not on the source capacitance of intracochlearacoustic sensor 750. Therefore, by using the charge amplifier as theinterface between intracochlear acoustic sensor 750 and the otherelectrical components of cochlear implant 700, all electronics may bepositioned remotely from the acoustic sensor. As shown in FIG. 7, thecomponents are hermetically sealed inside the implant module 720. Thisfeature provides a sound pickup system 780 that is entirely completelypassive and can be designed in the form of a shielded coaxial cable. Inthese embodiments of the present invention, cochlear implant 700 isreferred to as operating in a charge mode.

Returning to the diagram of FIG. 8, C represents the source capacitanceof the piezoelectric element of intracochlear acoustic sensor 750, whileQ represents the electric charge present on the center core electrode(not shown). Furthermore, C_(f) represents the feedback capacitance ofcharge amplifier 710. Therefore, V_(out) is the output voltage and isdetermined by V_(out)=Q/C_(f), which, as noted above, is independent ofthe source capacitance of the piezoelectric element within intracochlearacoustic sensor 750.

As noted above, embodiments of the present invention utilize apiezoelectric element to convert motion of the inner ear fluid intoelectrical charge. In specific embodiments, the piezoelectric elementcomprises a piezoelectric layer disposed about a core conductor. FIG. 9illustrates theoretical aspects related to the design of a piezoelectriclayer 962 that may be implemented in the embodiments described above. Asnoted, piezoelectric layer 962 has a cylindrical shape with a length Land a wall thickness t, and outer and inner radii of a_(o) and a_(i),respectively. Piezoelectric layer 962 is disposed about signal electrode964 which is a solid conductor core bonded onto the inner surface of thetube. Ground electrode 966 is a metallic film coated on the outersurface of piezoelectric layer 962, which also serves as the EMIshielding. Each of electrodes 964, 966 are made of biocompatible metalssuch as Pt, Au, or other suitable materials. The EMI shielding of signalelectrode 964 with ground electrode 966 may be beneficial given thepresence of electrical stimulation current in the cochlea.

Under certain circumstances, the structure of an intracochlear acousticsensor shown in FIG. 9 is similar to that of a coaxial cable. In suchcircumstances, the source capacitance of the intracochlear acousticC_(s) is given below by Equation (1) as:

$\begin{matrix}{C_{s} = \frac{2\;{\pi ɛ}\; L}{\ln\frac{a_{o}}{a_{i}}}} & (1)\end{matrix}$where ε is the permittivity of PVDF material.

The intracochlear acoustic sensor of the FIG. 9 may be analyzed in asubstantially similar manner as that previously used to analyze a smallcylindrical hydrophone as reported by Langevin (1954) and Barger andHunt (1964). See, Barger, J. E. and F. V. Hunt “Solid core probehydrophone.” J Acoust Soc Am 36(8): 1589-90 (1964); see also, Langevin,R. A. “The electro-acoustic sensitivity of Cylindrical Ceramic Tube.” J.Acoust. So. Am 26: 421-7 (1954). The model, experimentally verified byBarger and Hunt by constructing and testing probe hydrophones made ofPZT-5 ceramic cylinders with an outer diameter of 1/16^(th) inch and theradius ratio η of 0.68 is applied below.

Specifically, applying the above noted analysis, piezoelectric layer 962is assumed to be polarized radially through its thickness. Whenhydrodynamic pressure P_(i) is applied uniformly over the surface, twotypes of stresses are generated in piezoelectric layer 962 and in innersignal electrode 964. These stresses are described in the polar (r, θ)coordination system as the radial stress σ_(rt) and σ_(rc), and thetangential stress σ_(θt) and σ_(θc), respectively. Both the radial andtangential stress and displacement w can be expressed in Equations (2)below as:

$\begin{matrix}{{{\sigma_{rt} = {{Ar}^{- 2} + C}},{\sigma_{\theta\; t} = {{- {Ar}^{- 2}} + C}},\mspace{14mu}{{{and}\mspace{14mu}\sigma_{rc}} = {\sigma_{\theta\; c} = {E({const})}}}}{{w_{rt} = {\frac{1}{Y_{t}}\left\lbrack {{{- {A\left( {1 + v_{t}} \right)}}r^{- 1}} + {{C\left( {1 - v_{t}} \right)}r}} \right\rbrack}},\mspace{11mu}{{{and}\mspace{14mu} w_{rc}} = {\frac{1}{Y_{c}}{E\left( {1 - v_{c}} \right)}r}}}} & (2)\end{matrix}$where Y_(t) and Y_(c) are the Young's moduli; v_(t) and v_(c) are thePoisson's ratios of the tube and core, respectively. The A, C and E arethe constants to be determined by boundary conditions. See, Timoshenko,S. and J. Goodier, Theory of Elasticity, (1951) New York, McGraw-Hill.

Since piezoelectric layer 962 is bonded to signal electrode 964, thecontinuity of the radial stress and displacement at the boundary betweenthe inner surface of layer 962 and the outer surface of signal electrode964 requires the following given in Equation (3) as:σ_(rt)(r=a _(o))=−P _(i,)σ_(rt)(r=a _(i))=σ_(rc), andw _(rt)(r=a _(i))=w _(rc)(r=a _(i))  (3)where σ_(rt) and σ_(rc); w_(rt) and w_(rc) are the radial stress anddisplacement of piezoelectric layer 962 and signal electrode 964,respectively. By substituting Eq. (2) into (3), the radial andtangential stresses can be given by Equation (4) as:

$\begin{matrix}{{\sigma_{rt} = {\frac{- P_{i}}{1 + {\eta^{2}G}}\left\lbrack {{\eta^{2}{Ga}_{o}^{2}r^{- 2}} + 1} \right\rbrack}},\mspace{14mu}{\sigma_{\theta\; t} = {\frac{- P_{i}}{1 + {\eta^{2}G}}\left\lbrack {{{- \eta^{2}}{Ga}_{o}^{2}r^{- 2}} + 1} \right\rbrack}}} & (4)\end{matrix}$where η=a_(i)/a_(o), and

$\begin{matrix}{G = {\left\lbrack {\frac{Y_{c}\left( {1 - v_{t}} \right)}{Y_{t}\left( {1 - v_{c}} \right)} - 1} \right\rbrack/\left\lbrack {\frac{Y_{c}\left( {1 + v_{t}} \right)}{Y_{t}\left( {1 - v_{c}} \right)} + 1} \right\rbrack}} & (5)\end{matrix}$

Furthermore, the internal electrical field e_(r) radially through thethickness of piezoelectric layer 962 is given by Equation (6) as:e _(r) =g ₃₁σ_(θt) +g ₃₃σ_(rt)  (6)

Therefore, the open circuit voltage V_(o) generated between the innerand outer electrodes is given by Equation (7) as:

$\begin{matrix}{V_{o} = {{\int_{a}^{a}{e_{r}{\mathbb{d}r}}} = {\int_{a_{o}}^{a_{i}}{\left\lbrack {{g_{31}\sigma_{\vartheta\; t}} + {g_{33}\sigma_{rt}}} \right\rbrack{\mathbb{d}r}}}}} & (7)\end{matrix}$

By substituting Eq. (4) here, the open circuit voltage sensitivity ofthe Piezotube sensor can be found by Equation (8) as:

$\begin{matrix}{\frac{V_{o}}{P_{i}} = {\frac{{a_{o}\left( {1 - \eta} \right)}\left( {1 - {\eta\; G}} \right)}{1 + {\eta^{2}G}}\left\lbrack {{g_{33}\frac{1 + {\eta\; G}}{1 - {\eta\; G}}} + g_{31}} \right\rbrack}} & (8)\end{matrix}$

In certain embodiments of the present invention, the outer diameter ofan intracochlear acoustic sensor is less than 0.8 mm, which isapproximately the same diameter as that basal region of certainconventional electrode assemblies. The intracochlear length of a sensoris dependent on, for example, the flexibility of the structure. Inspecific embodiments, it may be assumed that an implantable acousticsensor is rigid, and that the intracochlear length is less than 8 mm.

Embodiments of the present invention have been primarily described withreference to using an intracochlear acoustic sensor as a primary soundpickup component. It would be appreciated that an intracochlear acousticsensor of the present invention may also be used in as component of asystem having other types of acoustic sensors. For example, theintracochlear acoustic sensor of the present invention may be used withone or more subcutaneous microphones, thereby enabling a choice ofmultiple types of acoustic inputs to be provided for a totallyimplantable cochlear implant system. Such an arrangement may improve theoverall performance of the totally implantable cochlear implant systemby providing a supplementary means of capturing sound, rather thanhaving to rely on the performance of the particular subcutaneousmicrophone(s) used. The multiple sensor system can also facilitate theselective use of different types of sensors in various environmentalconditions, where the users or the controlling software may selectdifferent settings for sensitivity, directivity and the like.

Further features and advantages of the present application may be foundin commonly owned and co-pending U.S. patent application Ser. No.10/986,812, filed Nov. 15, 2004, the content of which is herebyincorporated by reference herein. All documents, patents, journalarticles and other materials cited in the present application are herebyincorporated by reference.

The invention described and claimed herein is not to be limited in scopeby the specific preferred embodiments herein disclosed, since theseembodiments are intended as illustrations, and not limitations, ofseveral aspects of the invention. Any equivalent embodiments areintended to be within the scope of this invention. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

What is claimed is:
 1. An implant comprising: an intracochlear acousticsensor implantable in a recipient's cochlea comprising: an elongate coreconductor, and a piezoelectric element disposed on the surface of thecore conductor configured to detect pressure waves in the perilymph ofthe cochlea when the acoustic sensor is at least partially implanted inthe cochlea, and to produce electrical signals corresponding to thedetected pressure waves.
 2. The implant of claim 1, wherein thepiezoelectric element is a layer covering a length of the coreconductor.
 3. The implant of claim 2, further comprising: a surfaceelectrode covering a length of piezoelectric layer; and an externalpassivation layer covering a length of the surface electrode.
 4. Theimplant of claim 1, wherein the elongate core conductor comprises one ormore metallic wires.
 5. The implant of claim 1, wherein the coreconductor comprises a non-conductive core having a metallic coating on asection of the surface thereof, and wherein the metallic coating extendsthe length of the non-conductive core.
 6. The implant of claim 1,wherein the core conductor is a porous member.
 7. The implant of claim1, wherein a region of the piezoelectric element is polarized, andwherein a region of the piezoelectric element is unpolarized.
 8. Theimplant of claim 1, further comprising: a cable electrically connectingthe acoustic sensor to one or more components positioned outside therecipient's cochlea.
 9. The implant of claim 8, wherein the coreconductor extends through the cable to connect the acoustic sensor tothe one or more components.
 10. The implant of claim 8, wherein thecable comprises: an elongate wire extending between the core and the oneor more components.
 11. The implant of claim 10, wherein the elongatewire has a plurality of coils formed therein, and wherein the wire isdisposed in a flexible coating.
 12. The implant of claim 1, wherein saidpiezoelectric element is a piezo-polymer.
 13. The implant of claim 12,wherein the piezoelectric element is a polyvinylidene fluoride (PVDF) orPVDF copolymer film taped on the surface of, and spirally wound aroundthe core conductor.
 14. An implant, comprising: an intracochlearacoustic sensor implantable in a recipient's cochlea comprising: anelongate core conductor, a piezoelectric element disposed on the surfaceof the core conductor configured to detect pressure waves in theperilymph of the cochlea when the acoustic sensor is at least partiallyimplanted in the cochlea, and to produce electrical signalscorresponding to the detected pressure waves; and an electrode assemblyconfigured to deliver electrical stimulation signals, generated based onthe electrical signals produced by the piezoelectric element, to therecipient's cochlea.
 15. The implant of claim 14, wherein thepiezoelectric element is a layer covering a length of the coreconductor.
 16. The implant of claim 15, further comprising: a surfaceelectrode covering a length of the piezoelectric layer; and an externalpassivation layer covering a length of the surface electrode.
 17. Theimplant of claim 14, wherein the elongate core conductor comprises oneor more metallic wires.
 18. The implant of claim 14, wherein the coreconductor comprises a non-conductive core having a metallic coating on asection of the surface thereof, and wherein the metallic coating extendsthe length of the non-conductive core.
 19. The implant of claim 14,wherein the core conductor is a porous member.
 20. The implant of claim14, wherein a region of the piezoelectric element is polarized, andwherein a region of the piezoelectric element is unpolarized.
 21. Theimplant of claim 14, further comprising: a charge amplifier positionedoutside the recipient's cochlea; and a cable electrically connecting theacoustic sensor to the charge amplifier.
 22. The implant of claim 21,wherein the core conductor extends through the cable to connect theacoustic sensor to the charge amplifier.
 23. The implant of claim 21,wherein the cable comprises: an elongate wire extending between the coreconductor and charge amplifier.
 24. The implant of claim 23, wherein theelongate wire has a plurality of coils formed therein, and wherein thewire is disposed in a flexible coating.
 25. The implant of claim 14,wherein said piezoelectric element is a piezo-polymer.
 26. The implantof claim 25, wherein the piezoelectric element is a polyvinylidenefluoride (PVDF) or PVDF copolymer film taped on the surface of, andspirally wound around the core conductor.
 27. The implant of claim 14,wherein the electrode assembly and the implant comprise a unitarycomponent.